1. Field of the Invention
The present invention relates to an optical device provided with a function to correct blur in a captured image, a control method for the optical device, and an image capture apparatus equipped with the optical device.
2. Description of the Related Art
Shake correction devices mounted on optical devices such as lens barrels and interchangeable lenses as well as on image capture apparatus such as cameras and video cameras using the optical devices include an optical shake correction device adapted to drive some lenses (hereinafter referred to as shift lenses) in a group of image capture lenses in a direction perpendicular to an optical axis and make corrections by varying the optical axis. Such a shake correction device corrects blur in a captured image by driving the shift lenses so as to detect camera shake using an angular velocity sensor and correct the detected shake.
Examples of signal processing performed by the angular velocity sensor include a method such as is disclosed in Japanese Patent Laid-Open No. 2009-217075. The method involves amplifying an output of the angular velocity sensor using an amplifier, extracting an offset component from a signal thus obtained, changing a reference voltage of the amplifier, and thereby removing the offset component after the amplification. Variations in amplifier output caused when the reference voltage is changed is canceled out under microcomputer control in a subsequent stage.
However, with the conventional method, there arises a minute difference between a voltage generated when the reference voltage is changed and a voltage canceled out in the microcomputer. This is caused, for example, by a linear output error inherent to a D/A converter (hereinafter abbreviated to DAC) used to change the reference voltage or by resistance variation with temperature. However, such a minute difference is problematic in that it appears as image flicker on a telephoto side sensitive to correction. Thus, to reduce the flicker, it is necessary to minimize changes in the DAC output.
On the other hand, to secure a dynamic range of a signal concerning the camera shake detected by the angular velocity sensor, amplifier output in the absence of vibrations needs to be set to the center of a detectable voltage range by accurately removing offsets from the output of the angular velocity sensor. For that, it is necessary to change the reference voltage frequently.